Numerical and experimental study on the joint forming mechanism in the pneumatic splicing process

Abstract

This study presents an investigation on the joint forming mechanism of pneumatic splicing by numerical and experimental methods. A one-way coupling numerical model concerning interaction between fluid and filaments was established to simulate the complex motion of a flexible body in a spiral flow field. The airflow field in the splicing chamber, which contributes to longitudinal and normal aerodynamic force along a filament regarded as a digital chain composed of a series of interconnected rods, was obtained by a two-equation turbulent computational fluid dynamics model. Contact-friction behavior within filaments was also taken into consideration. An iterative algorithm was adopted to update the displacement of filaments and the corresponding aerodynamic force. A high-speed visualization test bench was built to record the sequence motion of filaments in the splicing process. The splicing mechanism within flexible filaments was identified by comparison between the experimental data and numerical results. The filament portion located in the homolateral rotating channel with respect to orifice is blown to bent by the jet airflow. It contributes to a frontal area in the axial airflow direction, causing the filament to be retracted toward its fixed end. Meanwhile, the portion in the contralateral rotating channel tries to wrap around the opposite filaments due to the spiral airflow. The interaction between filaments generates the contact force and related friction force, which commonly resists the retracting force exerted on the homolateral filament portion. The competition between the two forces determines whether the joint can be formed. Furthermore, the influence of the overlapping length on splicing behavior was discussed.

Modeling of yarn strength and its influencing factors in the pneumatic splicing process

“…Figure 2 shows the 3D model of the splicing chamber. The structure of the splicing chamber is the same as that of Zhou et al 21 It is a symmetrical structure, which consists of an inlet channel, two acceleration channels, two outlet channels and a rotary channel. When the compressed air enters the splicing chamber from the air source, the tail yarn at both ends is spun quickly and twisted into a new twist joint.…”

“…The mechanical state of the fibers in the yarn will change after the splicing process. The relationship between yarn strain and fiber strain under large strain can be expressed by 21 e r ¼ e y cos 2 h i À vsin…”

“…The mechanical state of the fibers in the yarn will change after the splicing process. The relationship between yarn strain and fiber strain under large strain can be expressed by 21 where the Poisson’s ratio v represents the ratio of radial strain to axial strain of the yarn. According to the principle of constant volume of yarn before and after stretching, the Poisson’s ratio v can be expressed by Equation (15) …”